Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is likely to have appeared first either during the Early Ordovician or Late Cambrian period. With approximately 250 species, the Eurypterida is the most diverse Paleozoic chelicerate order. Following their appearance during the Ordovician, eurypterids became major components of marine faunas during the Silurian, from which the majority of eurypterid species have been described. The Silurian genus Eurypterus accounts for more than 90% of all known eurypterid specimens. Though the group continued to diversify during the subsequent Devonian period, the eurypterids were heavily affected by the Late Devonian extinction event. They declined in numbers and diversity until becoming extinct during the Permian–Triassic extinction event 251.9 million years ago.
Eurypterus is an extinct genus of eurypterid, a group of organisms commonly called "sea scorpions". The genus lived during the Silurian period, from around 432 to 418 million years ago. Eurypterus is by far the most well-studied and well-known eurypterid. Eurypterus fossil specimens probably represent more than 95% of all known eurypterid specimens.
Hibbertopterus is a genus of eurypterid, a group of extinct aquatic arthropods. Fossils of Hibbertopterus have been discovered in deposits ranging from the Devonian period in Belgium, Scotland and the United States to the Carboniferous period in Scotland, Ireland, the Czech Republic and South Africa. The type species, H. scouleri, was first named as a species of the significantly different Eurypterus by Samuel Hibbert in 1836. The generic name Hibbertopterus, coined more than a century later, combines his name and the Greek word πτερόν (pteron) meaning "wing".
Carcinosoma is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Carcinosoma are restricted to deposits of late Silurian age. Classified as part of the family Carcinosomatidae, which the genus lends its name to, Carcinosoma contains seven species from North America and Great Britain.
Chasmataspidids, sometime referred to as chasmataspids, are a group of extinct chelicerate arthropods that form the order Chasmataspidida. Chasmataspidids are probably related to horseshoe crabs (Xiphosura) and/or sea scorpions (Eurypterida), with more recent studies suggest that they form a clade (Dekatriata) with Eurypterida and Arachnida. Chasmataspidids are known sporadically in the fossil record through to the mid-Devonian, with possible evidence suggesting that they were also present during the late Cambrian. Chasmataspidids are most easily recognised by having an opisthosoma divided into a wide forepart (preabdomen) and a narrow hind part (postabdomen) each comprising 4 and 9 segments respectively. There is some debate about whether they form a natural group.
Alkenopterus is a genus of prehistoric eurypterid classified as part of the family Onychopterellidae. The genus contains two species, A. brevitelson and A. burglahrensis, both from the Devonian of Germany.
Nanahughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Nanahughmilleria have been discovered in deposits of Devonian and Silurian age in the United States, Norway, Russia, England and Scotland, and have been referred to several different species.
Onychopterella is a genus of predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Onychopterella have been discovered in deposits from the Late Ordovician to the Late Silurian. The genus contains three species: O. kokomoensis, the type species, from the Early Pridoli epoch of Indiana; O. pumilus, from the Early Llandovery epoch of Illinois, both from the United States; and O. augusti, from the Late Hirnantian to Early Rhuddanian stages of South Africa.
Willwerathia is a genus of Devonian arthropod. It is sometimes classified as synziphosurine, a paraphyletic group of horseshoe crab-like fossil chelicerate arthropods, while some studies compare its morphology to an artiopod. Willwerathia known only by one species, Willwerathia laticeps, discovered in deposits of the Devonian period from the Klerf Formation, in the Rhenish Slate Mountains of Germany.
Tylopterella is a genus of eurypterid, a group of extinct aquatic arthropods. Only one fossil of the single and type species, T. boylei, has been discovered in deposits of the Late Silurian period in Elora, Canada. The name of the genus is composed by the Ancient Greek words τύλη, meaning "knot", and πτερόν, meaning "wing". The species name boylei honors David Boyle, who discovered the specimen of Tylopterella.
Parahughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Parahughmilleria have been discovered in deposits of the Devonian and Silurian age in the United States, Canada, Russia, Germany, Luxembourg and Great Britain, and have been referred to several different species. The first fossils of Parahughmilleria, discovered in the Shawangunk Mountains in 1907, were initially assigned to Eurypterus. It would not be until 54 years later when Parahughmilleria would be described.
Unionopterus is a genus of eurypterid, an extinct group of aquatic arthropods commonly known as "sea scorpions". Fossils have been registered from the Early Carboniferous period. The genus contains only one species, U. anastasiae, recovered from deposits of Tournaisian to Viséan stages in Kazakhstan. Known from one single specimen which was described in a publication of Russian language with poor illustrations, Unionopterus' affinities are extremely poorly known.
Legrandella is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Legrandella was regarded as part of the clade Prosomapoda. Fossils of the single and type species, L. lombardii, have been discovered in deposits of the Devonian period in Cochabamba, Bolivia.
Weinbergina is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Fossils of the single and type species, W. opitzi, have been discovered in deposits of the Devonian period in the Hunsrück Slate, Germany.
Synziphosurina is a paraphyletic group of chelicerate arthropods previously thought to be basal horseshoe crabs (Xiphosura). It was later identified as a grade composed of various basal euchelicerates, eventually excluded form the monophyletic Xiphosura sensu stricto and only regarded as horseshoe crabs under a broader sense. Synziphosurines survived at least since early Ordovician to early Carboniferous in ages, with most species are known from the in-between Silurian strata.
Wiedopterus is a genus of eurypterid, an extinct group of aquatic arthropods. The type and only species of Wiedopterus, W. noctua, is known from deposits of Early Devonian age in Germany. The generic name derives from the Wied river, which runs near the site of the initial discovery, and the species name, noctua, derives from Latin noctua (owl) which refers to the superficial resemblance of the carapace to an owl.
Borchgrevinkium is an extinct genus of chelicerate arthropod. A fossil of the single and type species, B. taimyrensis, has been discovered in deposits of the Early Devonian period in the Krasnoyarsk Krai, Siberia, Russia. The name of the genus honors Carsten Borchgrevink, an Anglo-Norwegian explorer who participated in many expeditions to Antarctica. Borchgrevinkium represents a poorly known genus whose affinities are uncertain.
Camanchia is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Camanchia was regarded as part of the clade Prosomapoda. Fossils of the single and type species, C. grovensis, have been discovered in deposits of the Silurian period in Iowa, in the United States. Alongside Venustulus, Camanchia is one of the only Silurian synziphosurine with fossil showing evidence of appendages.
Anderella is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Anderella was regarded as part of the clade Prosomapoda. Fossils of the single and type species, A. parva, have been discovered in deposits of the Carboniferous period in Montana, in the United States. Anderella is the first and so far the only Carboniferous synziphosurine being described, making it the youngest member of synziphosurines. Anderella is also one of the few synziphosurine genera with fossil showing evidence of appendages, but the details are obscure due to their poor preservation.
Forfarella is a genus of chasmataspidid, a group of extinct aquatic arthropods. Fossils have been discovered in deposits of the Early Devonian period. The single and type species, F. mitchelli, is known from one only specimen found in Scotland, in the United Kingdom. Known as BMNH In 60023, it is poorly preserved and its type locality is uncertain, although it might be the Kelly Den stream section near the village of Arbirlot.
